The present invention relates to a new process for interrogation of a detector of the concentration of combustible gas and a device for its implementation. Different types of explosimeters are known that measure the concentration of combustible gas in an atmosphere by catalytic combustion on a platinum filament. The catalytic combustion heats the platinum wire and varies the resistance of the wire. This resistance change can unbalance a Wheatstone bridge fed from a source of direct current if the filament is placed in the bridge, and this imbalance can be measured. A metal filament coated with a porous refractory material is also known as a suitable filament for such a detector.
A discontinuous interrogation of the detector is the method generally used, especially for automatic explosimeters. For certain gases, in particular methane, the result of an interrogation of the detector in an atmosphere having a large concentration of gas is normally constituted by the inversion of the measurement signal issued by the detector. A specific treatment of the filament is generally necessary to obtain this inversion.
The difficulty with single voltage interrogation systems is that using the inversion of the signal issued by the detector does not totally guarantee the certainty of a large concentration of combustible gas in the atmosphere considered, especially for automatic detectors with discontinuous interrogation. More precisely, it has been established that the phenomenon of measurement signal inversion is not reproducible and that certain detectors, even in new condition, can give ambiguous indications of the combustible gas concentration.